Carbon wakeboard advice

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#1

Hey guys,

Someone came to me and asked if I could make them a wakeb,oard with CF, and gave me a deck to copy the shape he wants. I have no idea what impacts these boards face, but I suspect it is a lot.

I think I will make a two part mould, and bond the two parts together as it would be easy to make moulds from the other board, but then I need to shape the foam core and that might be very time consuming. Are there any better methods that I could try? Or maybe try an expanding foam.

I’m not sure amout my layup schedule, I was thinking maybe
C -245gsm twill
C -150gsm UD +30°
C - 150gsm UD - 30°
Some core
C - 150gsm UD - 30°
C - 150gsm UD + 30°
C -245gsm twill

Would the UD be overkill? Should I just use 2 layers of twill each side instead?

I use axson epoxies for moulds and parts, can use hand layup and vacuum infusion.

Any advice would be appreciated

Regards
Jacques

#2

Once I molded a Kiteboard for making it in carbon for personal use but I never found the time to complete it. One thing you have to consider is that gluing the parts from a two part mold might leave air gaps within the part which is bad I guess.

#3

Thanks tnt. I will consider the impact of the air pockets.
what was your layup plans for the kiteboard?

No other takers for advice?

#4

I know kiteboards are made with 650gsm eglass triaxial…
2 times 150gsm carbon on each side would be quite stiff with a thick core. making the core thinner would be an option.

#5

You can check on Youtube there are many kite building videos.

#6

Hey dude built a boatload of these,
Think the board you’re making will be a little stiff (all depends on thickness though)

biggest design criteria is core crush. (trying to keep the top of the core from denting, delaming and then ultimately failing from compression buckling) Once this is accomplished board strength is really an afterthought, I found carbon has little advantage as it often makes the board either too stiff or too brittle.

4 layers of 6 oz eglass on top 0/90 45 45, 0/90 on divincell H80 3 layers bottom 0/90, 45, 090 you then use core thickness to get the desired stiffness A good stiff board often is rocking about .75" thick. in the center tapered on the outside and is pretty bombproof.

Cheapest way to make it is pour urethane rails or glue abs to the core for rails. Taper the core linearly with a router, lay it up on a curved piece of shinyness to get your rocker and then throw athin piece of abs on top to act as a top mold vacuum it down to take the shape of the table squeeze the resin out the sides and hand sand the rails.

However this process doesn’t work if you’re copying a board with channels.
Many companies use wood cores for cost and durability on sliders especially if the board has channels on the bottom. And they CNC the wood core to get these channels.

Wood gives a fair bit of stiffness, prevents any core crush, requires reduced thickness and fiber content making it an all around cheap option but heavy as all hell and a disgrace to all things made of composites.

So a couple of questions

  1. How thick is the board you wanna take a mold of
  2. Does the bottom have channels?
  3. Does it need to be light?
  4. Will they be hitting kickers and sliders?
#7

Yep, similar to above… i made many kiteboards years ago… i did clear carbon finish boards among others aswell…

The problem is, core crush under the foot area… divinicell h80kg/m3 (or similar) does not have anywhere near enough compressive strength properties in this area. Youd have to go upto something much higher density such as 250kg/m3 foam under the foot bindings area of the board, the rest you can use much lower density foam or other material- i know, because i had a few break before i knew this… Problem is, its very expensive and you only need a small amount so buying 1 full 2400x1200mm sheet will cost more than the entire project including labour… you might consider a foaming epoxy instead and pour you own, or perhaps a high density end grain balsa???

UD carbon i used in some boards, others not. It depends on the stiffness you trying to acheive. Youd have to ask the guy if he likes a stiff board or not. If he likes it stiff, use the UD carbon in the layup. If he likes flex, just use triax glass and overlay a light carbon woven cloth - which is only there to get the carbon look. Also, you have to use a resin with a high Tg or HDT as the carbon look gets extremly hot in the sun. It can generate enough heat to soften the resin and then it can warp the board… So choose your resin carefully if going for the carbon look, i used to use a vinyl ester for mine with a very high Tg…

As to the method, i used to vac bag them on a peice of 3mm aluminium sheet. I had a frame under it, and threaded rods so i could adjust the rocker in the aluminium. This limits you to a flat bottom with single rocker curve tho, no channels as the previous poster mentioned. If i was to do it again today, i would infuse them rather than vac bag it, and use a complete envelope bag if you need channels in the bottom. Shape the foam core accordingly. I used sheet PVC or ABS plastic as inserts for the foot bindings to thread into- resin will stick well to this plastic if you rough it up and quickly pass a gas flame over it to activate the surface even more.

To finish the board, after the bagging is cured, trim up the edges and peel off the peel ply, then i used to spray a low viscosity polyester resin directly onto it with a spraygun. It was a surfboard finishing resin to which i thinned with styrene monomer and added additional wax in styrene - i had to experment a bit with this in order to get slick results. After spraying, the finish was excellent and could hide the flash trim too. Sometimes the finish was a little hazy from the wax, but a quick buff and its super shiney… if i didnt use enough wax in the PE resin, sometimes there would be tacky areas remaining, so you need to do your own testing if you go this route. I figured it gave a more durable finish than a paint coating…

#8

Thanks for all the advice guys! This is more info than I ever expected!

The board he wants does have channels on the bottom, so that makes it a bit harder. The board is about 0.8 inches in the middle. I would like to make it as light as I can without compromising the structure, thus the carbon route. The board won’t be hitting sliders or kickers, he says he prefers wake. So maybe that helps me a bit.

I will have to rethink the core a bit, but I have an idea that I might try out on a test panel. I want to make a corrugated core from CF running the width of the board, formed between strips of HD foam, so that it can still flex a bit length wise. But I will make a test sample to test it for compression strength. I am looking for a way to still have some flex with the CF so I might drop a layer on the bottom.

This is a one-off project, so being labor intensive does not matter that much, as long as I can make something of quality. But being a novice with boards does make it quite a challenge.

I have only ever used epoxy resins, for its strength, and the one I use has a Tg (after post cure) of 170F, but its not UV resistant. Should I rather be looking at VE resins with a higher Tg?

Thanks again guys.

#9

Hi, I would suggest your layup should be nice and stiff but you might consider a kevlar or glass inside so if it does brake due to impact, it will stay in one piece so it could be repaired. As for the core, if you are using a closed mould unless you can shape a PU foam core exactly the right size, you should use and expanding foam. I use an epoxy 2 part foam because when it is post cured, it is a structural foam, adding to the stiffness. Polyurethane foam can be used and it is cheaper.
Regards,
Jim

#10

For UV protection you can finish it with a good UV resistant 2K Urethane clear, it’ll make the carbon texture pop a little nicer too

there are a lot of epoxies with UV inhibitors and some additives out there for other epoxy systems. System 3 sb 112 is the most commercially available UV resistant epoxy.

Haven’t built any with channels but if pour foam has enough compression resistance this would be an easy way to fill the negatives in the mold. .

Honestly wouldn’t stress too much, about getting compressive strength THATmuch better than d cell h80
been riding THE CRAP OUT OF a 3 x 6 oz, top and 3 x 6 oz bottom. eglass board with an extra patch over the foot beds and an H80 core for about 5 years now…

#11

Board mental, i started out using only H80 pvc foam thoughout the entire board… the boards broke under the foot by the heavier and more extreme riders… the light weight guys or the novice riders who didnt ride hard, never broke them with H80 under the foot… In order the solve the problem for the more extreme guys, i had to go upto a higher density core with a higher compressive strength. The amount of carbon in the skin layup, doesnt matter - i had a layup of around 600gsm triax carbon per side, this was all stiched reinforcement, not woven cloth - and this one guy still broke the boards (3 in total) until i figured out the core crush problem - the core crushes on landing a jump, and the laminate buckles in compression failure, always directly under the foot binding area. This board was a stiff as a peice of concrete due to the amount of carbon in it, i thought it would be impossible to break, but not so… my understanding of composite engineering was poor at that time…

There are epoxies available with a high Tg - up to you if you want to use epoxy, provided you put a UV topcoat over it will protect it, and epoxy has a higher elongation to break, so its better for strength in a flexible application. Otherwise, look at the vinylesters…

In this case with shape on both sides, i would shape the foam core into what the guy wants and get all the inserts in for the fins and foot bindings etc… Then i would envelope bag it and infuse it in one shot. If you use full peices of reinforcement, with no overlaps, which is easy with a small product like this, the finished board will be as fair as the foam you shaped. After you peel off the peel ply, simply spray it with a PU or PE resin as i described earlier, no sanding or fairing required…Kinda like the way i did this boat rudder;

[ame=“http://www.youtube.com/watch?v=5K4Rim_hD1o”]rudder infusion - YouTube[/ame]